[Konstantinos]

pawn Код:

RegisterPlayer(playerid, inputtext);

If you register with password "test", it will write to the file "test" for password. When it's time to login, you hash the password first and that's why they do not match.

Replace to:

pawn Код:

new hashPassword[129];
WP_Hash(hashPassword, 129, inputtext);
RegisterPlayer(playerid, hashPassword);